Another why

A white elephant is a supposedly valuable possession whose upkeep exceeds its usefulness, and it is therefore a liability. The term derives from the sacred white elephants kept by traditional Southeast Asian monarchs in Burma, Thailand, Laos and Cambodia. To possess a white elephant was regarded (and still is regarded, in Thailand and Burma) as a sign that the monarch was ruling with justice and the kingdom was blessed with peace and prosperity. The tradition derives from tales in the scriptures which associate a white elephant with the birth of Buddha.

One of the stories behind this was the circus owner PT Barnum bought one without seeing it first, and when he got it he foudn out that it wasn't white but splotchy and people did not want to pay money to see it. He wasn't able to get money from displaying it and he had to pay for its keep so it was an expensive possession that he gained no value from, and even had to keep paying more, later that term was applied to similar situations. I hope this helps.